The present invention relates to semiconductor integrated circuits, and more particularly to effective technology applicable to a one-chip microcomputer containing a programmable ROM (read only memory) in which an electric write operation can be performed by access from a microprocessor, for example.
An early one-chip microcomputer containing an EPROM (electrically programmable ROM) is exemplified in "Hitachi Microcomputer Data Book, 8-bit single chip" pages 823-865, published by Hitachi, Ltd. in August, 1984. Since the one-chip microcomputer includes EPROM, a user program can rapidly be provided, and can improve adaptability to mass production. That is, if a mask type ROM is used as the incorporated ROM, various masks for forming the program during manufacture may be implemented.
In recent years, so-called IC cards are being used in place of magnetic cards. An earlier one-chip microcomputer containing EEPROM (electrically erasable and programmable ROM) to be utilized in such an IC card or data bank is disclosed in "The Hitachi Hyoron" Vol. 68, No. 7, pages 29-32, published by Hitachi Hyoronsha on Jul. 25, 1986.
In this device, a write operation to the programmable ROM is not performed using the above mentioned writing apparatus. Instead, write operation to the programmable ROM must be performed directly by access from the microprocessor. In such an apparatus, the write operation in a definite time is performed by an incorporated logic circuit, such as oscillation circuit. Since process deviation of the incorporated non-volatile storage element is relatively large, the write time must be set in accordance with the worst case. Therefore, in many cases, additional, unnecessary write time will be spent.
An object of the invention is to provide a semiconductor integrated circuit device, such as a one-chip microcomputer containing a programmable ROM, to enable the write operation rapidly and securely.
The foregoing and other objects and novel features of the invention will be apparent from the description of the specification and the accompanying drawings.